This invention relates to drilling. More particularly, the invention relates to a method of extending the length of a drill string. It also relates to a drill string element and to a coupling member. It further relates to a shank rod and to a drill string.
In top hammer drilling, use is made of a hammer which rotates and applies an axial percussive load to a drill string in order to drill holes in the ground.
The drill string comprises a first member mounted in the hammer to which one or more extension rods are connected end-to-end. A drill bit is provided at the leading end of the drill string.
The first member, herein called a "shank rod", typically includes an elongate shank having a leading end and a trailing end. An annular collar is provided on the shank rod intermediate the leading end and the trailing end. At least part of the shank rod between the trailing end and the collar is non-circular in cross-section such that when a trailing end portion of the shank rod is positioned in the hammer, the hammer can engage the non-circular portion to rotate the drill string and apply axial percussive loads to the trailing end of the shank rod. The leading end of the shank rod is configured to be connected to a trailing end of the rearmost (uppermost) extension rod of the drill string.
As drilling proceeds and the drill string penetrates deeper into the ground it becomes necessary periodically to extend the length of the drill string. This is achieved by disconnecting the leading end of the shank rod from the trailing end of the rearmost (uppermost) extension rod, and connecting a leading end of a new extension rod to the trailing end of the rearmost extension rod and connecting a trailing end of the new extension rod to the leading end of the shank rod.
One disadvantage with this procedure is that it is relatively time consuming. A further disadvantage is that in certain applications, e.g., in stope drilling, space is restricted, which can make it extremely difficult to connect a new extension rod in position between the shank rod and the rearmost extension rod.
It is an object of this invention to alleviate these problems.